FIG. 1 shows a digital signal receiver used, for example, in infrared communications. The receiver 10 generally comprises: an amplifier 20 that receives a modulated (for example, ASK modulated) digital signal (i.e., from a photodiode or an antenna); a detector 30 that detects the signal amplified by amplifier 20 and extracts a baseband signal which is the direct current component thereof; an integration circuit 40 that integrates the baseband signal and outputs a reference signal which is the average value of the received signal; a comparator 50 that compares the voltage of the baseband signal and the voltage of the reference signal from integration circuit 40 and outputs the comparison result as a digital signal; and a signal detector 60 that processes the digital signal output from comparator 50.
With typical infrared communication, when meaningful data is transmitted a bit pattern or preamble is added to the header portion of the data. Accordingly, when a signal that includes meaningful data is received and signal detector 60 detects a signal with the preamble output from comparator 50, it determines that intended data has been received and outputs a digital signal. On the other hand, when signal detector 60 cannot detect a preamble, it concludes that meaningless data caused by noise has been received and does not output a digital signal. If the voltage of the reference signal for comparator 50 is lowered to improve the sensitivity of the receiver, the comparator 50 will detect slight noise or glitches included in the received signal; to generally overcome this problem, Japanese Kokai Patent Application No. 2004-135306 discloses a demodulator which imparts hysteresis to the reference signal, thus reducing erroneous operation.
With conventional receiver 10, though, it operates even when there is no signal; that is, when there is no meaningful data. Comparator 50 continues to output a digital signal, and signal detector 60 detects continuously monitors for a preamble. This continuous operation of the signal detector 60 and comparator 50 wastefully consumes power when no signal is present. Therefore, there is a need for a receiver with lower power consumption.